Wind as an Agent of Change Earth Science 11

Abrasion Mainly by sand grains (Windblown silt and clay particles are too small and too soft to wear away rock) Affects below 1 meter – formation of toadstool rocks

Wind as an Agent of Change Agent of erosion Most effective in dry areas (deserts) where sands, silts, and clays lie loose and dry Act in two ways: 1. Pick up and move sediment 2. Drive sediment against rocks and other materials

Wind as an Agent of Change Dust storm: When strong, steady winds lift great amounts of silt and clay from top soil

Wind as an Agent of Change Materials eroded: Fine grained materials (silt, clay, some sand) Materials usually moved close to ground Most wind erosion occurs in dry climates

Ventifact Sand blasted boulder The side of the ventifact that faces the steady wind direction wears into a smooth, flat surface or “facet”

Erosion Suspension: Clay and silt Saltation: Sand

Desert Pavement Pebbles and boulders left in a desert when the sand and silt are blown away 80% of the Sahara Desert Makes up the surface surrounding the ventifact Protects the materials beneath from further deflation

Deflation Removal of loose particles by wind

Blowout Small, shallow depressions formed by deflation Can be many thousands of meters long and a hundred meters deep

Wind Deposits 1. Loess: Made of unlayered, yellowish particles that are size of silt Common in China, N. Europe, and N. US Unlike ordinary silt, particles are angular in shape

Wind Deposits 2. Sand Dunes Hill of sand Form when sand piles up against shrubs, boulders, or other obstructions Require loose sand and strong winds Migrate downwind up to 30 m/yr burying oases, towns, farms Movement controlled with vegetation and fences

Types of Dunes

Assignment Read pages 177-181 Questions #1-6 on page 194